Field of Endeavor
The present application relates to additive manufacturing and more particularly to additive manufacturing of lithium microbatteries.
State of Technology
This section provides background information related to the present disclosure which is not necessarily prior art.
The article, “Material by Design,” Science and Technology Review, March 2012, provides the state of technology information reproduced below.
“From the Bottom Up
Additive manufacturing is the process of building 3D structures by sequentially layering one material on top of another in a desired pattern. It is a dramatic departure from more conventional fabrication techniques in which material is removed from a bulk piece through processes such as etching or machining. Contrary to what the name might imply, additive manufacturing actually requires less material than “subtractive” fabrication methods. It also results in less waste and can reduce manufacturing costs.
Over the last decade, additive manufacturing has become a burgeoning industry, enabling rapid prototyping of components for automotive, medical, and electronic applications. News headlines in recent years have showcased the often-remarkable capabilities of 3D printers that produce macroscale objects, such as a prototype musical instrument. Although specialized technologies are available for developing 3D structures with small, mesoscale (millimeter-length) features—hearing aids, for example—they are limited to a small number of materials as well as component size and shape specifications.
Building Complex Structures
Projection microstereolithography, direct ink writing, and electrophoretic deposition offer a unique combination of advantages for fabricating microscale structures from multiple materials. “These three technologies complement each other,” says Kuntz. “Where one is weaker in a certain capability, the others are strong.”
Projection microstereolithography, for example, can reliably create structures in three dimensions, but for now, it is compatible with only a few materials. Direct ink writing and electrophoretic deposition, on the other hand, work well with more materials but do not offer the same 3D capability as projection microstereolithography. Electrophoretic deposition would have to burn out excess, or fugitive, material within a fabricated component to create void space, but direct ink writing and projection microstereolithography can build these spaces where needed during component fabrication. Says Kuntz, “By combining the techniques, we can create more complex structures than we can produce using one method alone.”
With each fabrication approach, the team first applies a computer-aided design program to section an image of the desired structure into 2D slices in the horizontal plane. In a project with MIT professor Nicholas Fang and his colleague Howon Lee, the team used projection microstereolithography to display 2D images on a digital photomask made from a micromirror or liquid crystal on a silicon chip. An ultraviolet light-emitting diode illuminates the miniature display, which reflects light and an image of the component to be fabricated through a series of reduction optics onto a photopolymer liquid resin. As the resin cures, it hardens into the shape of the image. The substrate holding the resin is then lowered using a motion-controlled stage, and the next 2D slice is processed.
Projection microstereolithography is a high-speed parallel process that can fabricate structures at both micro- and macroscales within minutes. “Using projection microstereolithography, we can rapidly generate materials with complex 3D microscale geometries,” says Spadaccini, the principal investigator for the technique.
However, the method does have its limitations. “The quality of a component depends on the uniformity of light at the image or polymerization plane and both the lateral and depth resolution of the system,” he says. “Resolution is restricted both by the optical resolution and the physical-chemical characteristics of the exposed monomer solution.”
Inking a Material
The direct ink-writing process can also create micro- to macroscale structures with extreme precision. With this technique, a print head mounted to a computer-controlled translation stage deposits inks into programmed designs on various substrates. The process works layer by layer, adding a continuous filament to a substrate. The patterns it generates range from simple, one-dimensional wires to complex, 3D structures.
Inks are administered through one or more nozzles, and filament diameter is determined by nozzle size, print speed, and rates of ink flow and solidification. The time required to build a final part is determined by the distance from the nozzle to the substrate and by print speed. The finest feature size obtained with this technology is approximately 200 nanometers—smaller than the features produced with projection microstereolithography. Recently, the team constructed two direct ink-writing platforms that can travel 30 centimeters at up to 10 centimeters per second while maintaining micrometer and submicrometer resolution.
Direct ink writing can rapidly pattern different materials into multiscale, multidimensional structures for an array of applications. However, process improvements, including more sophisticated inks, are needed to achieve the arbitrary, complex 3D structures required for designer materials. To date, the researchers have designed particle- and nonparticle-based inks derived from metals, ceramics, and polymers.”
U.S. Pat. No. 4,575,330 to Charles W. Hull for apparatus for production of three-dimensional objects by stereolithography issued May 11, 1986 provides the state of technology information reproduced below.
“It is common practice in the production of plastic parts and the like to first design such a part and then painstakingly produce a prototype of the part, all involving considerable time, effort and expense. The design is then reviewed and, oftentimes, the laborious process is again and again repeated until the design has been optimized. After design optimization, the next step is production. Most production plastic parts are injection molded. Since the design time and tooling costs are very high, plastic parts are usually only practical in high volume production. While other processes are available for the production of plastic parts, including direct machine work, vacuum-forming and direct forming, such methods are typically only cost effective for short run production, and the parts produced are usually inferior in quality to molded parts.
In recent years, very sophisticated techniques have been developed for generating three-dimensional objects within a fluid medium which is selectively cured by beams of radiation brought to selective focus at prescribed intersection points within the three-dimensional volume of the fluid medium. Typical of such three-dimensional systems are those described in U.S. Pat. Nos. 4,041,476; 4,078,229; 4,238,840 and 4,288,861. All of these systems rely upon the buildup of synergistic energization at selected points deep within the fluid volume, to the exclusion of all other points in the fluid volume, using a variety of elaborate multibeam techniques. In this regard, the various approaches described in the prior art include the use of a pair of electromagnetic radiation beams directed to intersect at specified coordinates, wherein the various beams may be of the same or differing wavelengths, or where beams are used sequentially to intersect the same points rather than simultaneously, but in all cases only the beam intersection points are stimulated to sufficient energy levels to accomplish the necessary curing process for forming a three-dimensional object within the volume of the fluid medium. Unfortunately, however, such three-dimensional forming systems face a number of problems with regard to resolution and exposure control. The loss of radiation intensity and image forming resolution of the focused spots as the intersections move deeper into the fluid medium create rather obvious complex control situations. Absorption, diffusion, dispersion and defraction all contribute to the difficulties of working deep within the fluid medium on any economical and reliable basis.
Yet there continues to be a long existing need in the design and production arts for the capability of rapidly and reliably moving from the design stage to the prototype stage and to ultimate production, particularly moving directly from computer designs for such plastic parts to virtually immediate prototypes and the facility for large scale production on an economical and automatic basis.
Accordingly, those concerned with the development and production of three-dimensional plastic objects and the like have long recognized the desirability for further improvement in more rapid, reliable, economical and automatic means which would facilitate quickly moving from a design stage to the prototype stage and to production, while avoiding the complicated focusing, alignment and exposure problems of the prior art three dimensional production systems.”
U.S. Pat. No. 8,591,602 to Messaoud Bedjaoui for a lithium microbattery comprising an encapsulating layer and fabrication method issued Nov. 26, 2013 provides the state of technology information reproduced below.
Microbatteries, also called “all solid-state batteries”, find numerous industrial applications in particular in the field of microelectronics wherein component miniaturization and autonomy requirements impose the use of increasingly small, more powerful storage batteries with longer lifetimes. Microbatteries come in the form of a stack of solid thin layers successively deposited on a substrate by conventional techniques of the microelectronics industry in particular by physical vapor deposition (PVD), chemical vapor deposition (CVD) and lithography techniques.
Lithium microbatteries are particularly interesting on account of their high mass density, their high effective surface of energy storage and their low toxicity. Nevertheless, these lithium microbatteries are very sensitive to air and in particular to moisture. In the presence of water or oxygen, the lithium negative electrode oxidizes to respectively give lithium hydroxide (LiOH) or lithium oxide (Li.sub.2O). This phenomenon in the long run leads to a loss of the microbattery performances. To remedy this shortcoming, the microbattery is generally covered with an impermeable coating, compatible with the microbattery components, which encapsulates the lithium microbattery and thereby forms a barrier against contaminants. The commonly used barrier layers are polymer, ceramic or metal layers.
Other shortcomings also limit the use of these microbatteries in microelectronics or affect their performances. The thermal instability of lithium at high temperature is a particularly limiting point for integration of lithium microbatteries in microelectronic devices.
Finally, operation of the lithium microbattery being based on transportation of the current by the lithium ions, when the microbattery is charged and discharged, the electrodes undergo deformations due to insertion and extraction, also called de-insertion, of the lithium ions in the electrodes. These repeated modifications of volume rapidly cause mechanical damage, in particular losses of contact between the negative electrode and the corresponding current collector.
The article “Ionic Conductivity Enhancement of Polymer Electrolytes with Ceramic Nanowire Fillers,” by Wei Liu, Nian Liu, Jie Sun, Po-Chun Hsu, Yuzhang Li, Hyun-Wook Lee, and Yi Cui, Nano Lett., 2015, 15 (4), pp 2740-2745, Mar. 17, 2015, provides the state of technology information reproduce below.
Solid-state electrolytes provide substantial improvements to safety and electrochemical stability in lithium-ion batteries when compared with conventional liquid electrolytes, which makes them a promising alternative technology for next-generation high-energy batteries. Currently, the low mobility of lithium ions in solid electrolytes limits their practical application. The ongoing research over the past few decades on dispersing of ceramic nanoparticles into polymer matrix has been proved effective to enhance ionic conductivity although it is challenging to form the efficiency networks of ionic conduction with nanoparticles. In this work, we first report that ceramic nanowire fillers can facilitate formation of such ionic conduction networks in polymer-based solid electrolyte to enhance its ionic conductivity by three orders of magnitude. Polyacrylonitrile-LiClO4 incorporated with 15 wt % Li0.33La0.557TiO3 nanowire composite electrolyte exhibits an unprecedented ionic conductivity of 2.4×10−4 S cm−1 at room temperature, which is attributed to the fast ion transport on the surfaces of ceramic nanowires acting as conductive network in the polymer matrix. In addition, the ceramic-nanowire filled composite polymer electrolyte shows an enlarged electrochemical stability window in comparison to the one without fillers. The discovery in the present work paves the way for the design of solid ion electrolytes with superior performance.